1. Field of the Invention
The present invention relates to magnet-based sensors and in particular magnet-based magnetostrictive sensors.
2. Description of the Prior Art
Magnetostrictive transducers having elongated waveguides that carry torsional strain waves induced in the waveguide when current pulses are applied along the waveguide through a magnetic field are well known in the art. A typical linear distance measuring device using a movable magnet that interacts with the waveguide when current pulses are provided along the waveguide is shown in U.S. Pat. No. 3,898,555.
Devices of the prior art of the sort shown in U.S. Pat. No. 3,898,555 also have the sensor element in a housing which also houses the electronics to at least generate the pulse and receive the return signal. The amplitude of the return signal detected from the acoustical strain pulse is, as well known in the art, affected by many parameters. These parameters include the position magnet strength, waveguide quality, temperature, waveguide interrogation current, and assembly tolerances.
Several types of magnetic-based sensors are available for measuring linear or rotary position. Magnetic-based sensors have an advantage in that they provide non-contact sensing; so there are no parts to wear out. Examples of magnetic-based sensors are LVDTs, inductive sleeve sensors, and magnetostrictive sensors.
Magnetostrictive transducers require that their waveguide be interrogated with electric current. This magnetically energizes the waveguide, thereby launching the ultrasonic strain pulse that is detected at the end of the unit. When the strain pulse is converted to an electrical signal, it is referred to as the “return signal.” The time between the interrogation pulse and the detection of the return signal defines location of position magnet.
Normally, the interrogation current in the waveguide flows in one direction for a short period of time (one to three microseconds) prior to detection at the return signal.
It is an object of the present invention to combine magnetostrictive interrogation pulses additionally to increase the amplitude of the return signal.
It is another object of the present invention to provide a magnetostrictive interrogation pulse voltage with a lower voltage power supply.